1. Field of the Invention
The present invention relates to a black matrix of resin, as a constituent member of a color filter for, e.g., displays of color TV sets and personal computers, method for producing the black matrix of resin, method for producing a color filter using the same black matrix, and liquid crystal element using the color filter produced by the same method.
2. Related Background Art
One of the conventional methods for producing color filters for color-displaying liquid crystal elements is the so-called proximity exposure followed by development to produce patterns, where a negative color resist formed on a transparent substrate is irradiated with light at a certain exposure via a photomask apart from the resist at a certain distance (proximity exposure gap). Exposure is normally set at 100 mJ/cm2 or more, to sufficiently cure the resist.
Recently, use of black matrix as a black resist has been investigated, in order to shield light between adjacent colored portions in a color filter. A black matrix is a resist dispersed with light-shielding pigment, e.g., carbon black. As a result, the resist cannot sufficiently pass light for pattern exposure, and is considered to need an exposure of several hundreds mJ/cm2 (higher than that for the above-mentioned color resist) to be cured. In addition, the black resist contains larger quantities of sensitizer and reaction initiator than a pigment-free resist, in order to enhance its exposure sensitivity. Therefore, it is cured with a small quantity of light, e.g., diffracted light, making it difficult to accurately transfer an opening in a photomask to produce patterns.
One of the methods to solve the above problems involved in production of black resists is disclosed by Japanese Patent Application Laid-Open No. 3-252622. It tries to control uneven film thickness after development by exposure from the back side of a color filter coated with a black resist after having formed the color filter, and also instantaneous exposure from the front side and simultaneous patterning to improve surface strength. In this method, shape of the black matrix depends on color filter forming accuracy, although essentially free of the problems caused by diffracted light. Moreover, this method is inapplicable to an ink jet type color filter production method, because it forms a colored section (filter) using a black matrix of resin as the wall to prevent color contamination, and hence formation of the black matrix must precede that of the colored section.
The black matrix for production of active matrix type liquid crystal elements incorporating a thin-film transistor (TFT), the so-called TFT type liquid crystal elements, tends to have an opening of complex shape, because of importance of resistance of the TFT to light and brightness of the color filter. The black matrix for TFT type liquid crystal elements is shaped in such a way to make part of the line patterns finer, in order to shield light for the TFT and secure a required opening ratio. The photomask for forming such complex patterns involves complex patterns of diffracted light, and complex and distorted outer appearance shape of the exposed section of the resist. It is therefore not suited as a product.
Contact exposure, i.e., exposure with no gap between the photomask and resist, can prevent the problems caused by diffracted light. However, it is inadequate for mass production of color filters, because of problems, e.g., contamination of the masks and reattachment of dust to resist surfaces, when it is adopted for color filters being continuously produced.
As discussed above, pattern exposure of a negative black resist by proximity exposure also gives rise to exposure around a mask opening by diffracted light, causing problems, e.g., distortion of developed black matrix patterns and excessively increased line width.
It is an object of the present invention to solve the above problems and produce a black resist faithfully reflecting photomask shapes by reducing the effects of diffracted light in proximity exposure. It is another object of the present invention to provide a high-quality color filter and liquid crystal element using the above black resist.
The method of the present invention for producing a black matrix of resin is characterized in that it comprises 3 steps of forming a resist on a substrate, exposing the above resist at an exposure of 14.0 to 70.0 mJ/cm2 via a photomask, and developing the exposed resist to produce a pattern.
The method of the present invention can produce a pattern faithfully reflecting mask shapes, even when opening shape of a black matrix is complex with irregularities.